recshuffle.cpp

/*---------------------------------------------------------
 * Program: recshuffle.cpp
 * Usage: ./recshuffle
 *---------------------------------------------------------
 * Description: Prints a random permutation of the string
 * "helloworld" alongside the source string. This program 
 * uses a recursive approach instead of an iterative one
 *_________________________________________________________
 */


/* INCLUDES */
#include <iostream>
#include <stdlib.h>


/* NAMESPACE FUNCTIONS */

// allows "free" use of string class, endl and cout from the namespace std
using std::string;
using std::cout;
using std::endl;


/* FUNCTIONS */

/*----------------------------------------------------------------------------------------
 * Function: stringrandr()
 * Usage: string result = stringrandr(string source, string &result, int len, int curlen)
 *----------------------------------------------------------------------------------------
 * Description: Converts the empty string "result" into
 * a random permutation of the string "source" by
 * shuffling the contents of the prevous string. Source
 * remains untouched while result is modified and must 
 * be passed by reference. This function is recursive.
 *________________________________________________________________________________________
 */

string stringrandr(string source, string &result, int len, int curlen) {
	
	// base case; If this runs, the function ends.
	if (source == "" && curlen == 0)
		return result;

	// stores random index generated
	int index;
	
	// seed rand
	srand(time(NULL));

	// retrieves random index
	index = rand() % curlen;

	// appends the random char to new string
	result += source[index]; 

	// remove char from source
	source.erase(index,1);

	// recursive call
	return stringrandr(source, result, len, curlen-1);

}

int main () {

	// source and result strings used
	string s = "helloworld";
	string random = "";

	// length of source string used
	int slen = s.length();

	// produces a permutation of the string s
	random = stringrandr(s, random, slen, slen);

	// prints results and length of both strings
	cout << "Source String: " << s << endl << "New String: " << random << endl;
	cout << "Length of source: " << slen << endl << "Length of result: " << random.length() << endl;
}